1. Field of the Invention
The present invention relates to paper-making machines, and, more particularly, to pressing apparatus in a paper-making machine.
2. Description of the Related Art
In the press section of a paper-making machine, water is typically removed mechanically by passing the paper web through a nip between structural components, such as two rotating rolls. The nascent paper web is carried on a felt for absorbing the water expressed from the paper web as it passes through the nip.
One of the characteristics of a quality paper product is uniformity of caliper in a cross-machine direction of the paper-making machine. Such uniformity of caliper is difficult to obtain, particularly in bulky products, such as tissue and towel grades, due to deflection of machine components caused by gravity.
Rolls of different design, such as control-deflection rolls and plain rolls, deflect different amounts along their lengths extending in a cross-machine direction. A non-uniform gap, or uneven gap loading in the cross-machine direction, will produce undesirable variations in both caliper and moisture in the web passing through on its way to the dryer section. Such variations undesirably affect the processing of the web, such as by requiring costly special profiling downstream of the press section, increasing expensive thermal removal moisture in the dryer section, or slowing the entire paper-making machine.
It is also known to provide an air press within a paper making machine for the purpose of expressing water from the paper web. Pressurized air within an air chamber exerts pressure against the fiber web for pressing moisture from the fiber web. Air presses have not been widely used because it is difficult to maintain pressure within the air chamber as the fiber web travels through the air press at an operating speed.
What is needed in the art is a way of effectively sealing an air press to inhibit air leakage during operation.
The present invention provides a seal comprising at least a circular contoured outer surface of a hard material for engaging a belt disposed over a paper web which in turn is disposed over a felt carried on the surface of a support roll having a similar circular contoured surface which establishes an extended nip contact between the seal and support roll outer surfaces.
The invention comprises, in one form thereof, a seal for use in an air press for dewatering a traveling paper web in a paper-making machine, the air press including a support roll having a cylindrical surface, a belt and felt for supporting the paper web on either side thereof, an arm for mounting the seal, a seal body having a curved outer surface contour for substantially conforming to the curve of the cylindrical surface of the support roll, and an inner surface adjacent to the arm. A leading edge surface intersects with the curved outer surface, the leading edge surface defining the initial engagement with the traveling belt when in an operating position. A trailing edge surface intersects with the curved outer surface. The trailing edge surface defines, with the leading edge surface, the upstream and downstream bounds of the extended nip of the curved outer surface contour of the seal body over the support.
An advantage of this invention is the provision of a new and efficient cross-machine seal for use in an air press in a paper-making machine.
Another advantage is the provision of a seal for an air press which has a concave outer surface for engaging a traveling belt over a support roll surface.
Still another advantage is the provision of a seal which has at least an outer surface comprising a ceramic material.